JP2006106979A - Fingerprint image pickup unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a fingerprint image where the contrast of light and dark is recognizable with proper brightness in a range including fingerprint information necessary for personal identification being a primary section. <P>SOLUTION: This fingerprint image pickup unit is provided with a light source 3 for irradiating a fingertip section 1 having fingerprint 11 being the object of image pickup as a subject with the rays of light 30 which can pass through the subject, an image pickup means 5 for picking up the image of the rays of light from the light source passing through the subject, and for obtaining a fingerprint image where the projected section of the fingerprint is dark and the recessed section of the fingerprint is bright, and an optical system 4 for making the image pickup means form the image of the rays of light from the light source passing through the subject. The center of irradiation of the rays of light 30 from the light source 3 is set on almost the center line of the width direction on a face where the nail 12 of the fingertip section 1 is present and at the opposite side of the nail section against the nail line, so that almost any section other than the nail can be irradiated with the rays of light 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fingerprint image capturing apparatus, and in particular, a fingerprint capable of obtaining a stable fingerprint image even when the fingerprint unevenness is unclear regardless of the moisture state of the fingerprint skin surface. The present invention relates to an image pickup apparatus.

  In a conventional fingerprint image pickup apparatus, a finger is held in a non-contact state with a fingerprint portion of a fingertip portion, light is irradiated from the back side (back side) of the fingertip portion, and light transmitted through the inside of the finger is detected. Since the transmittance of light transmitted through the fingertip portion is higher in the concave portion than in the convex portion of the fingerprint, an image in which the concave portion is brighter than the convex portion of the fingerprint is obtained (for example, see Patent Document 1).

JP 2003-85538 A (page 3-4, FIG. 1-4)

  The conventional fingerprint image pickup apparatus is configured as described above, and can obtain a stable fingerprint image even when the fingerprint unevenness is unclear, regardless of the moisture state of the fingerprint skin surface. However, there is a case where the brightness is partially saturated or too dark, and there is a portion where the contrast of light and dark corresponding to the unevenness of the fingerprint is not known, and there is a case where the accurate fingerprint information cannot be obtained.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fingerprint image imaging apparatus capable of obtaining a fingerprint image with an appropriate brightness and a clear contrast between light and dark within a range including fingerprint information necessary for personal identification, which is a main part. is there.

  A fingerprint image capturing apparatus according to the present invention uses a fingertip portion having a fingerprint to be imaged as a subject, a light source that irradiates the subject with light that can pass through the subject, and a light source that passes through the subject. An imaging unit that captures light and obtains a fingerprint image in which a convex portion of the fingerprint is dark and a concave portion is bright; and an optical system that forms an image on the imaging unit of light from the light source that is transmitted through the subject. The irradiation center of the light is on the substantially center line in the width direction on the surface where the nail of the fingertip portion exists and on the opposite side to the nail portion with respect to the hairline of the nail. The part is irradiated.

According to the fingerprint image capturing apparatus of the present invention, a fingertip portion having a fingerprint to be imaged is a subject, the subject is irradiated with light from a light source that can pass through the subject, and the subject is irradiated with an optical system. The light from the light source that passes through the specimen is imaged on the imaging means, and the light from the light source that passes through the subject is imaged by the imaging means to obtain a fingerprint image in which the convex portion of the fingerprint is dark and the concave portion is bright. Regardless of the state of moisture on the skin surface of the fingerprint, a stable fingerprint image can be obtained even when the unevenness of the fingerprint is unclear.
Moreover, the light that can pass through the subject is on the substantially center line in the width direction on the surface of the fingertip where the nail exists, and on the opposite side of the nail from the nail line. In this case, since the portion other than the substantially nail is irradiated, a fingerprint image can be obtained in which the contrast of light and dark is known with appropriate brightness within a range including fingerprint information necessary for personal identification, which is a main part.
Therefore, more accurate fingerprint information can be obtained.

  The inventors of the present invention use a fingertip portion having a fingerprint to be imaged as a subject, irradiate the subject with light from a light source that can pass through the subject, and transmit the subject through an optical system. The light from the light source is imaged on an imaging means, and the light from the light source that passes through the subject is imaged by the imaging means to obtain a fingerprint image in which the convex portions of the fingerprint are dark and the concave portions are bright. It was discovered that the position of irradiating the light affects the shading of the fingerprint image. Mainly when the nail is irradiated, the toe side is saturated and the base side becomes dark, and when it is irradiated to a part other than the nail near the nail, the whole shading of the fingerprint image becomes gentle, and when it is irradiated near the first joint, the base side Was found to be brighter and the toe side darkened.

The inventors used the bone as the second light source, and the light hitting the bone was scattered at a wide angle and transmitted through the fingertip part to the fingerprint part with relatively uniform intensity. Because it is not, I guess that if the light from the light source is mainly applied to the nail, the light that did not hit the bone will be transmitted as it is and the shading will be tightened.
As a result, it is possible to capture a fingerprint image with reduced shading by irradiating light to a portion other than the substantially nail near the nail line, and a range including fingerprint information necessary for personal identification, which is a main part I thought that it would be possible to contribute to the optimization of lightness.

  In the present invention, the range including fingerprint information necessary for personal identification is, for example, the region from the first joint of the finger to the fingertip, the region including the first joint portion, or the fingerprint on the side of the finger. Refers to the included area.

Embodiment 1 FIG.
1 and 2 are diagrams for explaining a fingerprint image imaging apparatus according to Embodiment 1 of the present invention. More specifically, FIG. 1 is a side view showing the overall configuration of the fingerprint image imaging apparatus, and FIG. FIG. 6 is a bottom view showing a state in which the vicinity of the fingertip portion is viewed from the imaging means side (abdominal side).

In the fingerprint image capturing apparatus according to the present embodiment, the fingertip portion 1 having the fingerprint 11 to be imaged is the subject, and the light 30 that can pass through the subject 1 is present in the presence of the nail 12 whose irradiation center is the fingertip portion 1. A light source 3 that is on a substantially center line in the width direction on the surface that is on the opposite side of the nail 12 with respect to the hairline of the nail 12, and irradiates a portion other than the substantially nail 12;
Imaging means 5 for imaging the light 30 from the light source 3 that passes through the subject 1 to obtain a fingerprint image corresponding to the fingerprint 11 in which the convex portion of the fingerprint 11 is dark and the concave portion is bright;
An optical system 4 for imaging the light from the light source 3 that passes through the subject 1 on the imaging means 5;
A fingerprint image output from the imaging means 5 is subjected to image processing to obtain fingerprint information, and a signal processing unit 6 for identifying an individual based on the fingerprint information is provided.
Furthermore, means for adjusting the brightness of the image by adjusting at least one of the light irradiation conditions (luminance and irradiation region 16) and the gain of the image pickup means 5 (image pickup element 52) (lightness determination unit 66, light source drive circuit 32, Gain adjustment circuit 55),
Means (image processing unit 62) for superimposing or partially pasting a plurality of fingerprint images of different brightness on the same subject.

  In the present embodiment, a subject holding portion that can hold the fingertip portion 1 (in FIG. 1, a subject holding portion with an opening that can hold the fingertip portion 1 in a state where the surface of the fingerprint 11 to be imaged is not in contact with the fingertip portion 1 is provided. 2) is provided. The opening portion of the subject holding unit 2 with the opening is provided so as to include an observation surface 100 that is a range imaged by the imaging means 5.

  The fingertip portion 1 that is a subject has a fingerprint 11 to be imaged on the ventral side, and the fingerprint 1 has a concavo-convex pattern composed of a convex portion (mountain portion) and a concave portion (valley portion). In the present invention, the fingertip portion 1 refers not only to the tip portion of the finger, but also from the tip portion of the finger to the vicinity of the first joint or the second joint.

The light source 3 that irradiates the fingertip part 1 with light 30 that can be transmitted through the fingertip part 1 causes the light to travel from the dorsal side (nail side) opposite to the fingerprint 11 of the fingertip part 1 to the ventral side (fingerprint side). Is provided. As the light source 3, light having a main wavelength in the red light to near infrared light region, that is, projection light of any wavelength (monochromatic) in the red light to near infrared light region, or red light to near infrared light. Projection light in which light over a region is mixed, or light that emits light in the red wavelength to near infrared light region (monochromatic or mixed in some cases) as a main wavelength is used. For example, a laser, a light emitting diode, or a lamp light source is used. Light in the red light to near-infrared light region is preferably used because of its high light transmittance with respect to the living body that is the subject 1, but more preferably has a main wavelength in the range of 600 nm to 1400 nm. Furthermore, since the light absorption characteristic of hemoglobin in the blood vessel is minimum at around 660 nm, in order to reduce the influence of the blood vessel on the fingerprint image, light in a region where the main wavelength is 630 nm to 780 nm is more preferable.
Further, the fingertip portion 1 and the light source 3 may be covered with a light shield so as not to be affected by light from the outside.

The light source 3 is composed of one or more lasers, light emitting diodes, and lamp light sources, for example, and can be turned on at an arbitrary number at the same time. The fingertip unit 1 is held by the subject holding unit 2 with an opening, and is arranged so as to irradiate a predetermined region 16 when the observation surface 100 is in a position that fits within the opening of the subject holding unit 2 with an opening. In addition, the light source driving circuit 32 is configured to control the irradiation condition (luminance and irradiation region 16) of the light 30 irradiated to the subject 1 by controlling the element to be turned on. For example, when the light source 3 is composed of a plurality of light emitting elements, each element or a small group of elements configured to irradiate the same position (area) irradiates different positions (areas) of the fingertip 1. The position to be irradiated is controlled so that the element to be lit can be changed according to the position (region) to be irradiated, or when the light source 3 does not have a plurality of light emitting elements and is single You may control to move to (area | region).
Note that controlling the irradiation region 16 includes both position control and region size control.

The fingerprint image capturing apparatus according to the present embodiment includes a marker light source 33 that irradiates the subject 1 with marker light 31 for positioning the subject 1.
In the marker light source 33, when the fingertip portion 1, which is a subject, is placed on the subject holding portion 2 with an opening and covers the opening, the marker light 31 does not enter the imaging element 52, and the subject light holding portion 2 with the opening is exposed. It is installed so that the marker light 31 is incident on the image sensor 52 in a state where the fingertip portion 1 is not placed.
Further, when the subject 1 is moved so that the marker light 31 is irradiated to a predetermined position of the subject (fingertip portion) 1, the subject 1 is arranged at a position where the light from the light source 3 is irradiated to the irradiation region 16. can do.
The marker light source 33 may be shared with the light source 3, but as the marker light 31, for example, a curve along an arrow or a nail skin, or other meanings that can be understood by humans and help to understand the position where the finger is held up A certain pattern may be projected from one light source to one or several places.
Further, the wavelength of the marker light 31 is not limited to the red light to near-infrared light region, but may be visible light that can be viewed by the user.

The optical system 4 forms an image on the image sensor 52 with light from the light source 3 that passes through the convex portion of the fingerprint 11 on the fingertip 1 and light from the light source 3 that passes through the concave portion of the fingerprint 11. In the present embodiment, the optical system 4 is telecentric on the object side (subject 1 side) through which the transmitted light from the fingertip unit 1 first passes through the lens 41 and the transmitted light passes next to the lens 41. A diaphragm 42 is provided at such a position.
In order to obtain a clearer fingerprint image, the lens 41 is mainly provided with a telecentric effect, and a lens that mainly contributes to image formation is installed at a position where light passes after passing through the aperture 42. An optical system composed of a plurality of lenses may be configured by installing a lens having an effect of taking image distortion.

  The ventral side of the fingertip part 1, that is, the surface of the fingerprint 11 to be imaged is a curved surface, and the distance between the fingerprint 11 and the image sensor 52 varies depending on the location in the observation surface 100. Image distortion due to differences may occur. Therefore, by increasing the depth of focus so that the entire surface of the observation surface 100 is in focus and adopting a telecentric optical system on the object side, fingerprints with improved contrast without being affected by defocusing or magnification fluctuations. An image can be obtained.

  In the image pickup means 5 (hereinafter also referred to as the image pickup system 5), a fingerprint corresponding to a fingerprint is picked up by picking up an image formed by the optical system 4 with light having an intensity distribution transmitted through the internal tissue of the fingertip portion 1. Get an image. The imaging unit 5 includes a wavelength selection element 51 as a wavelength selection unit, an imaging element 52, and an image output circuit 53 that converts an electrical signal from the imaging element 52 into an electrical image signal.

The wavelength selection element 51 (wavelength selection means) selectively transmits only light having the same wavelength as that of the light source 3 (red light to light in the near-infrared light region). For example, an interference filter, filter glass, or plastic filter is used. The output optical signal from the wavelength selection element 51 is imaged by the imaging element 52.
In FIG. 1, the wavelength selection unit 51 is provided between the diaphragm 42 and the image sensor 52. The wavelength selection unit 51 includes a plurality of lenses 41 between the lens 41 and the fingertip unit 1. It may be provided at any position such as between the lens and the lens 41 and the stop 42 when the lens is used. Further, a lens 41 or an image sensor 52 having a wavelength selection function can also be used.

  The imaging element 52 is, for example, a two-dimensional solid-state imaging element such as a CCD (charge imaging element) or a CMOS (complementary metal oxide semiconductor) image sensor, an imaging tube, or the like. The image sensor 52 is sensitive to light passing through the fingertip part 1 and transmitted through the internal tissue of the fingertip part 1, that is, having sensitivity to light in the red light to near infrared light region. The imaging means 5 is shielded from receiving light other than light from the fingertip portion 1. In addition, a gain adjustment circuit 55 that adjusts the gain of the image sensor 52 is provided.

The signal processing unit 6 includes an image capturing unit 61 that receives a signal from the image output circuit 53, an image processing unit 62 that processes the signal from the image capturing unit 61 and performs binarization and thinning, and the image processing unit 62. A fingerprint data storage unit 63 that receives a signal from the image data and stores it as a registered image, and a personal identification unit 64 that performs personal identification by comparing the image from the image processing unit 62 with the image from the fingerprint data storage unit 63. The fingerprint image output from the image output circuit 53 is subjected to image processing to obtain fingerprint information, and an individual is identified based on the fingerprint information.
Furthermore, the signal processing unit 6 processes the signal from the image capturing unit 61, determines whether the signal is within a predetermined threshold range, determines whether the finger is present, and the light source driving circuit A finger presence determination unit 65 that can send a signal to 32 is provided.
The image capture unit 61 has a function of temporarily storing the captured fingerprint image.

Furthermore, the signal processing unit 6 determines whether the brightness of the fingerprint image captured by the image capturing unit 61 is within a predetermined threshold range, and based on the determination result, the light source driving circuit 32 and the gain adjustment circuit. And a lightness determination unit 66 that adjusts at least one of the irradiation condition (intensity, irradiation region 16) of the light 30 from the light source 3 that irradiates the fingertip unit 1 and the gain of the image sensor 52. ing. That is, the brightness determination unit 66 determines the image brightness of the entire image of the fingerprint image, the entire range where fingerprint information necessary for personal identification can be obtained, a region where a part of the region is extracted, or a divided region. Can be determined.
In addition, in the case where a plurality of images are captured for the same subject with at least one of the irradiation condition and the gain of the imaging means, the brightness determination circuit 66 may determine the brightness of the image every time imaging is performed. For example, the brightness of a plurality of areas is determined by a single determination and the result is stored. After that, the brightness of the image is calculated from the stored result without performing the brightness determination again so that each determined area is appropriate. It can also be adjusted.

  Further, in addition to the above-described processing such as binarization and thinning, the image processing unit 62 performs imaging by changing at least one of the irradiation condition of the light 30 to the subject 1 and the gain of the imaging means (imaging element 52). It also has a function of superimposing or partially pasting a plurality of fingerprint images.

  Note that it is not necessary that all of the parts provided in the signal processing unit 6 are provided in the signal processing unit 6. For example, the image output circuit 53 is connected to a personal computer and a part thereof is provided therein. For example, when the fingerprint data is stored but personal identification is not performed, the personal identification unit 64 can be omitted.

Next, the relationship between the irradiation region (position) of the light 30 from the light source 3 and the brightness of the obtained fingerprint image will be described with reference to FIGS.
3 to 6 are diagrams showing fingerprint images picked up by the CCD when the light (laser light) 30 is spot-irradiated on the points A to D in FIG. 7, and FIG. 3 shows a point A in FIG. 4 shows a fingerprint image when the laser beam 30 is irradiated to the point B in FIG. 7, FIG. 5 shows the point C in FIG. 7, and FIG. 6 shows the point D in FIG. 3 to 6, the right side in the figure is the toe side (the tip side of the fingertip portion 1). FIG. 7 is a diagram illustrating irradiation points A to D of the light 30 on the back side of the fingertip portion 1.
In FIG. 3, the brightness is almost uniform over the entire fingerprint image, but in FIG. 4, the toe side (tip side of the fingertip part) near the irradiation region 16 (point B) is saturated, and FIG. The toe side far from the point C) is dark. As for the width direction of the fingertip portion 1, it can be seen from FIG. 6 that the portion near the irradiation region 16 (point D) is saturated and the opposite side is dark.

  From these results, in order to obtain a fingerprint image with substantially uniform brightness over almost the entire surface including the fingerprint information necessary for personal identification, the point A in FIG. It can be seen that it is preferable to irradiate a portion other than the substantially nail 12 on the substantially center line in the width direction on the surface where the nail exists and on the opposite side of the nail 12 with respect to the nail 12.

More specific irradiation areas 16 include, for example, point A (spot area) in FIG. 7, first irradiation area 161, second irradiation area 162, and third irradiation area 163 shown in FIG. 8. .
The first irradiation region 161 is a region in which the longitudinal direction extends from the point P at the nail to the first joint in the root direction, and the width does not exceed the width of the fingertip part 1. There is a center in the longitudinal direction at a position of about ½ of the length to one joint.
The second irradiation region 162 has a longitudinal direction at a position that is approximately ¾ of the length from the point P at the base side of the nail to the first joint in the longitudinal direction. The region is slightly at the tip, and the width is approximately 1/3 of the finger width, and the center in the longitudinal direction is at a position approximately 1/3 of the length from the point P at the nail to the first joint.
The third irradiation region 162 has a longitudinal direction at a position that is approximately 1/5 of the length from the point P at the base side of the nail to the first joint in the longitudinal direction. The region is slightly at the tip, and the width is approximately 1/5 of the finger width, and the center in the longitudinal direction is at a position approximately 1/10 of the length from the point P at the nail to the first joint.
In addition, although it is preferable that the edge part of the front end side of a longitudinal direction corresponds with the point P at the time of a nail | claw, you may catch on the nail | claw 12 to some extent. If the length from the point P at the nail to the tip of the fingertip part 1 is L, the tip end on the tip side in the longitudinal direction is preferably about 1/3 of the length L from the point P at the nail. Preferably it is up to about 1/4, and more preferably the upper nail skin (the part corresponding to the cuticle of the nail).

  Furthermore, examples of the shape of the irradiation region 16 include an oval shape and a rectangular shape inscribed in the region.

  Further, since near infrared light has a low transmittance in the blood of the living body, the blood vessel pattern inside the fingertip portion 1 is superimposed on the concave-convex pattern of the fingerprint 11 in the fingerprint image output from the imaging means 5, and the brightness decreases. It may cause a decrease in contrast. When a part that is extremely darker than the others is seen, it is also possible to take an image with a strong shading in order to brighten the part. For example, when the image brightness of the part on the toe side of the fingertip part 1 is low, the light 30 from the light source 3 is intentionally irradiated so as to cover the nail 12, and the brightness and the gain of the image pickup device are adjusted as necessary. If the image of the part 1 with the low lightness of the image on the toe side is imaged so that the lightness is appropriate, the contrast of the low lightness part can be improved. In this way, the shading can be controlled by moving the irradiation region (position) of the light 30 to the fingertip portion 1, and partial contrast can be improved.

Next, the operation will be described.
First, the marker light 31 is turned on with a light amount that is easy to see, and the image sensor 52 captures images at predetermined intervals.
When the fingertip part 1 is moved so that the marker light 31 is irradiated to a predetermined position and the fingertip part 1 blocks the marker light 31, the marker light 31 that has been captured by the image sensor 52 is blocked. The obtained image has a certain range below a certain brightness. An image obtained by the image sensor 52 is captured from the image output circuit 53 to the signal processing unit 6 by the image capturing unit 61 of the signal processing unit 6. Further, a predetermined range on the image sensor 52 (image obtained by the image sensor 52) that is sent from the image capturing unit 61 to the finger presence determination unit 65 and is blocked by the fingertip unit 1. If the lightness is within a predetermined threshold range, it is determined that the fingertip portion 1 exists in the imaging range of the imaging device 52.

  At the same time, the user moves the fingertip part 1 while visually confirming that the marker light 31 hits the optimum position of the fingertip part 1, so that the irradiation position optimization of the light 30 of the light source 3 to the fingertip part 1 is performed. It is also possible to optimize shading and increase the efficiency of the irradiation light quantity with respect to the image brightness.

When the finger presence determination unit 65 determines that the fingertip unit 1 is in the imaging range of the image sensor 52, the finger presence determination unit 65 sends a signal to the light source driving circuit 32 to project the light 30 that can pass through the fingertip unit 1, and from the light source 3. The light source 3 is turned on by adjusting the number of elements to be turned on and the brightness per element so that the light 30 has a predetermined brightness. The marker light source 33 may be turned off when the light source 3 is turned on, or may be turned on as it is.
The light 30 irradiated on the back surface (the surface opposite to the fingerprint 11) of the fingertip part 1 passes through the inside of the finger and reaches the fingerprint 11. The internal tissue near the surface on the ventral side of the fingertip part 1 has a transmittance distribution corresponding to the unevenness of the fingerprint 11 on the surface, and the light transmittance of the internal tissue corresponding to the convex part of the fingerprint is low, and the internal structure corresponding to the concave part Since the light transmittance of the tissue is high, the brightness of the light transmitted through the latter is higher than that of the former.

  Lens 41 and diaphragm 42 of optical system 4 optically designed so that light having an intensity distribution according to fingerprint 11 that has passed through fingertip 1 is telecentric toward the object (fingertip 1 that is the subject). Thus, an image is formed on the image sensor 52. A wavelength selection element 51 is disposed between the aperture 42 and the imaging element 52, and only light having the same wavelength as that of the light source 3 (red light to near-infrared light region) is selected. The image output circuit 53 receives an electrical signal from the image sensor 52, and outputs a fingerprint image having a valley (concave portion) brighter than a crest portion (convex portion) of the fingerprint as an image electrical signal.

  The fingerprint image obtained in this way by the imaging means 5 is captured by the image capturing unit 61 provided in the signal processing unit 6 and sent to the image processing unit 62. The image processing unit 62 performs image processing such as binarization and thinning on the fingerprint image as described in Japanese Patent Laid-Open No. 10-334237, for example, and extracts fingerprint feature information (fingerprint information). The extracted data is stored in the fingerprint data storage unit 63 as necessary. The personal identification unit 64 compares the data output from the image processing unit 62 with the data stored in the fingerprint data storage unit 63 to identify an individual.

Next, adjustment of the brightness of the fingerprint image and superposition or partial pasting of a plurality of fingerprint images having different brightness values taken on the same subject will be described.
In the present embodiment, the light 30 from the light source 3 is used in order to obtain a fingerprint image in which light and dark contrast is known with appropriate brightness in a range including fingerprint information necessary for personal identification, which is a main part of the fingerprint image. The irradiation center is on the approximate center line in the width direction on the surface of the fingertip portion 1 where the nail 12 is present and on the opposite side of the nail 12 from the nail 12, except for the nail 12. (Irradiation region 16 such as the first to third irradiation regions 161 to 163 described above) is irradiated.

However, there is still a part where the peak and valley of the fingerprint cannot be distinguished because the brightness is saturated or the brightness is too low in the range that contains the fingerprint information necessary for personal identification, which is the main part of the fingerprint image. In some cases, the fingerprint image cannot extract information necessary for personal identification.
Therefore, in the present embodiment, for example, before the image processing unit 62 extracts the feature information of the fingerprint, the lightness determination unit 66 determines whether the lightness of the fingerprint image is excessive or insufficient, and the lightness is excessive or insufficient. In order to obtain an image having an appropriate brightness, the image is picked up again by adjusting at least one of the irradiation condition (the luminance of the light source 3 and the irradiation area) and the gain of the image sensor 52 so as to collect an image having an optimal brightness. I have to.

  In addition, in order to obtain appropriate brightness within the range that includes fingerprint information necessary for personal identification, which is the main part of the fingerprint image, it is possible to take multiple images by adjusting multiple times instead of adjusting only once. is there. In addition, even when the range including the fingerprint information necessary for personal identification, which is the main part of the above-described fingerprint image, satisfies the appropriate brightness, the image quality can be further improved and the contrast can be improved. Adjustment and imaging may be repeated several times.

Hereinafter, a case where a plurality of images are collected will be described as an example. Light 30 is emitted from the light source 3 at a predetermined brightness and irradiation region 16, and the first imaging is performed with a predetermined gain of the image sensor 52. The image is sent from the image capturing unit 61 to the lightness determination unit 66, where the overall lightness of the range including the fingerprint information necessary for personal identification, which is the main part of the fingerprint image, is determined. As described above, at least one of the brightness adjustment of the light source 3 by the light source drive circuit 32 and the adjustment of the irradiation region and the gain adjustment by the gain adjustment circuit 55 is performed, and imaging is performed again.
Here, the overall brightness is determined based on the overall brightness not including position information for each pixel such as a histogram, or the brightness of a narrow range such as the brightness of a specific part or a small number of profiles. It refers to a case and may include a part that is partially too bright or too dark.

An image in which the overall brightness of the area including the range including the fingerprint information necessary for personal identification, which is the main part of the fingerprint image, is divided into a plurality of partial areas by the brightness determination unit 66, and the image of each partial area Judge the brightness. The plurality of partial areas include various areas such as each area obtained by dividing the entire area into two parts such as the tip side and the base side, and a plurality of areas including at least one pair of at least a fingerprint crest and valley from the entire area. Can be considered.
When all of the plurality of partial areas obtained in this way satisfy appropriate brightness within a predetermined threshold range, the image information of the image is sent to the image processing unit 62 for personal identification or fingerprint data Extract fingerprint information for storage.

  Further, in each partial area, when there is at least one location where the brightness of the image is outside the predetermined threshold range, the light source driving circuit 32 causes the entire partial area to have an appropriate brightness. Imaging is performed again after performing at least one of the adjustment of the luminance of the light source 3, the irradiation area, and the gain adjustment by the gain adjustment circuit 55, the image is captured from the image capturing unit 61, and temporarily stored. The above operation is performed over all the partial areas where there is at least one location where the brightness of the image is outside the predetermined threshold range, and the obtained image is temporarily stored in the image capturing unit 61.

  Next, the temporarily stored image is sent from the image capturing unit 61 to the image processing unit 64, and a partial region that satisfies a proper brightness within a range of a predetermined threshold is superimposed or superimposed with a plurality of images. Processing such as cutting out and pasting them together is performed to obtain an image with appropriate brightness over the entire surface including fingerprint information necessary for personal identification.

  In the above-described example, a plurality of images with appropriate overall brightness of a region including a range including fingerprint information necessary for personal identification, which is a main part of the fingerprint image, or brightness of a predetermined specific part are appropriate. The image brightness of each partial area is determined by dividing it into partial areas, and it is determined whether or not to capture a plurality of images. However, the irradiation conditions and the imaging are determined from the beginning without determining the image brightness of each partial area. A plurality of images having different brightness values with at least one of the gains of the element 52 may be captured.

  In this case, for example, two or more lightness threshold values at the time of the first lightness determination after the first imaging are determined, and the brightness and irradiation of the light source 3 are set to obtain the image lightness corresponding to each threshold value. There is a method of imaging a plurality of images by determining the position, the irradiation area, and the gain value of the image sensor 42. In other words, a threshold value that makes the entire surface of the range including fingerprint information necessary for personal identification appropriate brightness, a threshold value that eliminates too dark parts instead of being brighter than appropriate brightness, and appropriate brightness A threshold value that eliminates the saturated portion instead of darkening can be considered. The plurality of images obtained in this way are superimposed or bonded as described above to form one image.

  In any of the above-described examples, in the case of the first imaging, the light source 3 is used to obtain a fingerprint image with almost uniform brightness over almost the entire surface including the fingerprint information necessary for personal identification. As described above, the irradiation center of the light 30 is on the substantially center line in the width direction on the surface of the fingertip portion 1 where the nail 12 is present, and on the opposite side of the nail 12 from the hairline of the nail 12 Therefore, it is preferable to irradiate a portion other than the substantially nail 12 (irradiation regions 16 such as the first to third irradiation regions 161 to 163 described above).

  Note that the image that is superimposed or pasted by the image processing unit 62 may be an image before processing such as binarization or an image after processing.

  In addition, when a plurality of images with different brightness values captured with respect to the same subject as described above are superimposed or pasted together, it is important to shorten the imaging interval as much as possible in order to prevent positional deviation of the fingertip 1.

  In the above description, a case has been described in which a plurality of images with different brightness captured on the same subject are superimposed or laminated. However, the light 30 from the light source 3 is used as the first to third irradiation regions 161 as described above. A fingerprint image obtained by irradiating the irradiation region 16 such as ˜163 is determined to have an appropriate overall brightness in a range including fingerprint information necessary for personal identification, which is a main part of the fingerprint image. May be used for personal identification.

  As described above, according to the present embodiment, the fingertip portion 1 having the fingerprint 11 to be imaged is the subject, the light source 3 that irradiates the subject with the light 30 that can pass through the subject, and the subject. An imaging unit 5 that captures the light from the light source 3 that is transmitted to obtain a fingerprint image in which the convex portion of the fingerprint 11 is dark and the concave portion is bright, and an optical system that forms an image on the image sensor 52 from the light source 3 that passes through the subject. 4, and the light 30 from the light source 3 has an irradiation center substantially on the center line in the width direction on the surface of the fingertip portion 1 where the nail 12 exists and the nail 12 portion with respect to the hairline of the nail 12. Since it is on the opposite side and irradiates the part other than the nail 12, it is possible to obtain a stable fingerprint image even when the irregularities of the fingerprint 11 are unclear regardless of the moisture state of the skin surface of the fingerprint 11. Necessary for personal identification, which is the main part of the fingerprint image. It is possible to obtain a fingerprint image brightness contrast is seen at the right luminosity in a range that includes the fingerprint information, it is possible to obtain accurate fingerprint information lightness preventing deterioration of the fingerprint image due cause.

  A means (lightness determination unit 66, light source drive circuit 32, gain adjustment circuit 55) for adjusting the brightness of the image by adjusting at least one of the light irradiation condition and the gain of the imaging means 5 (imaging device 52); Since it includes means (image processing unit 62) for superimposing or partially pasting a plurality of fingerprint images of different brightness on the same subject, it includes fingerprint information necessary for personal identification, which is the main part of the fingerprint image In this range, it is possible to obtain a fingerprint image in which the contrast of brightness and darkness can be obtained with a more appropriate brightness, and it is possible to more reliably prevent deterioration of the fingerprint image due to the brightness and to obtain more accurate fingerprint information.

  In addition, the fingerprint image output from the imaging means 5 is subjected to image processing to obtain fingerprint information, and the signal processing unit 6 for identifying an individual based on the fingerprint information is provided. Improved personal identification.

  In the above embodiment, the case where the lens 41 is used as the imaging unit has been described. However, a pinhole having an imaging function may be used in addition to the imaging lens.

Further, in the above embodiment, since near infrared light has low transmittance in the blood of living body, the blood vessel pattern inside the fingertip portion 1 is superimposed on the fingerprint uneven pattern in the fingerprint image output from the imaging means 5. Yes. Therefore, the blood vessel pattern may be removed from the fingerprint image output from the imaging means 5 as follows.
That is, first, a fingerprint image output from the imaging unit 5 is used as an original image, and a smoothing process is performed on the original image to obtain a smoothed image. Since the uneven pattern of the fingerprint has a narrower line width than the blood vessel pattern, the uneven pattern of the fingerprint is removed and the blood vessel pattern remains in the smoothed image. When the difference calculation between the original image and the smoothed image is performed, a fingerprint image in which only the concave / convex pattern of the fingerprint remains is obtained, and the feature information of the fingerprint is extracted from the fingerprint image.

  In the above description, the case where the fingerprint image obtained by the imaging means 5 is processed by the signal processing unit 6 to identify an individual has been described. However, even if the fingerprint image is simply obtained without identifying the individual. Needless to say, it is good.

  In order to reduce the overall size of the apparatus, as shown in FIG. 9, a plane mirror 8 is installed as a reflecting means so as to deflect the light transmitted through the fingertip 1, and the optical system 4, the wavelength selection element 51, and the imaging. The element 52 may be installed so as to face the deflected light. In FIG. 9, the signal processing unit 6 is omitted.

Note that the reflecting means is not limited to the plane mirror 8, and for example, a curved mirror can be used to reduce image distortion and aberration.
Further, a plurality of reflecting means may be provided to further reduce the size.
Further, the plane mirror 8 does not necessarily need to be between the lens 42 and the fingertip unit 1, and may be between the image sensor 42 and the fingertip unit 1, for example, between the lens 41 and the diaphragm 42.

  In FIG. 1, the fingertip portion 1 is arranged such that the ventral fingerprint 11 surface is substantially parallel to the imaging surface of the image sensor 52, but the fingerprint 11 surface of the fingertip portion 1 and the image sensor 52 The imaging surface may be arranged so as to have an angle. In this case, the same effect can be obtained.

  The subject holding unit 2 that can hold the surface of the fingerprint to be imaged in a non-contact state is not limited to the one having the frame shape shown in FIGS. 1 and 2, for example, as shown in FIG. A rod-shaped object arranged to support the fingertip part 1 near the first joint outside the observation surface 100 of the fingertip part 1 or an observation surface 100 sandwiched outside the observation surface 100 as shown in FIG. Can be used as at least a pair of rods arranged opposite to each other.

Embodiment 2. FIG.
FIG. 12 is a diagram for explaining the fingerprint image capturing apparatus according to the second embodiment of the present invention. More specifically, FIG. 12 is a side view showing the overall configuration of the fingerprint image capturing apparatus. In the following, differences from the first embodiment will be mainly described.

In the present embodiment, the subject holding unit 2 is not the subject holding unit 2 with an opening that can hold the fingertip unit 1 shown in the first embodiment while the surface of the fingerprint 11 to be imaged is in a non-contact state. A transparent object holding part 2 (hereinafter referred to as a transparent object holding part) 2 without an opening that can hold the fingertip part 1 in a state where the surface of the fingerprint 11 to be imaged is in contact is used. Unlike the first embodiment, the other configuration is the same as that of the first embodiment.
The operation is also the same as in the first embodiment, and the same effect as in the first embodiment can be obtained.

  However, in order to obtain a fingerprint image in which the convex portion of the fingerprint 11 is dark and the concave portion is bright by imaging the light from the light source 3 that transmits the convex portion of the fingerprint 11 and the light from the light source 3 that transmits the concave portion of the fingerprint 11 On the fingerprint contact surface of the subject holding unit 2, the critical angle of total reflection determined by the refractive index of the gas between the fingerprint recess and the transparent subject holding unit 2 and the refractive index of the transparent subject holding unit 2 is below. It is necessary to detect light incident on the transparent object holding part 2 in the direction of.

Embodiment 3 FIG.
In each of the above-described embodiments, the case where the subject holding unit 2 that can hold the fingertip unit 1 has been described. However, the subject holding unit 2 may not necessarily be provided.
The present embodiment is different from the first embodiment in that the subject holding unit 2 is not provided and the fingertip portion corresponding to the subject is not in contact with the structure, and other configurations are the same as in the first embodiment. Same as 1.
Even in such a configuration, the same effect as in the first embodiment can be obtained.

It is a side view which shows the whole structure of the fingerprint image imaging device by Embodiment 1 of this invention. It is a bottom view which shows a mode that it concerns on Embodiment 1 of this invention and looked at the finger-tip part vicinity from the ventral side. It is a figure which concerns on Embodiment 1 of this invention and shows the fingerprint image imaged by CCD. It is a figure which concerns on Embodiment 1 of this invention and shows the fingerprint image imaged by CCD. It is a figure which concerns on Embodiment 1 of this invention and shows the fingerprint image imaged by CCD. It is a figure which concerns on Embodiment 1 of this invention and shows the fingerprint image imaged by CCD. It is a figure which concerns on Embodiment 1 of this invention and shows the irradiation points AD of the light to the back side of a fingertip part. It is a figure explaining the irradiation area | region concerning Embodiment 1 of this invention. It is a side view which shows another whole structure of the fingerprint image imaging device by Embodiment 1 of this invention. It is a side view which shows another structure of the principal part of the fingerprint image imaging device by Embodiment 1 of this invention. It is a side view which shows another structure of the principal part of the fingerprint image imaging device by Embodiment 1 of this invention. It is a side view which shows the whole structure of the fingerprint image imaging device by Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fingertip part, 11 Fingerprint, 12 Nail, 16 Irradiation area, 2 Subject holding part, 3 Light source, 31 Marker light, 32 Light source drive circuit, 33 Marker light source, 4 Optical system, 41 Lens, 42 Diaphragm, 5 Imaging means, 51 wavelength selection element, 52 imaging element, 53 image output circuit, 55 gain adjustment circuit, 6 signal processing unit, 61 image capture unit, 62 image processing unit, 63 fingerprint data storage unit, 64 personal identification unit, 65 finger presence determination unit , 66 Lightness determination unit, 8 plane mirror.

Claims (3)

A light source that irradiates the subject with light that can pass through the subject, with the fingertip portion having a fingerprint to be imaged as the subject,
An imaging means for imaging the light from the light source that passes through the subject to obtain a fingerprint image in which the convex portion of the fingerprint is dark and the concave portion is bright;
An optical system that forms an image on the imaging means of light from the light source that passes through the subject,
The light from the light source has an irradiation center substantially on the center line in the width direction on the surface where the nail of the fingertip portion is present and on the opposite side to the nail portion with respect to the hairline of the nail. A fingerprint image imaging device characterized by irradiating other portions. Means for adjusting the brightness of the image by adjusting at least one of the light irradiation condition and the gain of the imaging means;
2. The fingerprint image capturing apparatus according to claim 1, further comprising means for superimposing or partially pasting a plurality of fingerprint images having different brightness on the same subject. 3. A fingerprint image imaging apparatus according to claim 1, further comprising a signal processing unit that obtains fingerprint information by performing image processing on the fingerprint image output from the imaging unit and identifies an individual based on the fingerprint information. .